Magnet wires having polyvinyl formal, acrylic, or polyimide insulation, have long been topcoated with either epoxy, polycarbonate, polyvinyl butyral, phenoxy, or polypropylene, to provide improved oil and abrasion resistance, as taught by Koerner et al., in U.S. Pat. No. 3,822,147, and Hilker et al., in U.S. Pat. No. 3,842,192. An additional quality, sometimes required, is a self-bondable outer adhesive varnish layer. These outer layers are fusible, acting as an adhesive, and after a coil is wound, the windings may be heated to bond the conductors into a unitary mass.
Sattler, in U.S. Pat. No. 3,412,354, taught catalyzed, amine-modified epoxy resins as an outer adhesive coat. Seki et al., in U.S. Pat. No. 4,129,678, taught a three layer, oil resistant, adhesive outercoat system, consisting of a polyimide, polyamide imide, or polyesterimide insulation base, a polyvinyl formal or epoxy resin intermediate layer, and an outer adhesive layer consisting of a mixture of high molecular weight phenoxy resin, with either an epoxy resin, a polyester, or a stabilized isocyanate, generally catalyzed with amine or BF.sub.3 -amine complex. The intermediate layer is taught as necessary to provide adequate adhesive properties. These catalyzed adhesive layers are usually applied in a process separate from the base and intermediate layers, usually at a lower temperature and higher speed, requiring the use of two heating tower operations, adding significantly to cost. Also, the use of catalysts in the adhesive layer, even at low solvent evaporation temperatures, may cause premature set-up, lowering subsequent adhesiveness. What is needed is a one-step process, utilizing overcoats that retain maximum adhesiveness after application and solvent evaporation, and show even more improved oil resistance.